1. Field of the Invention
The present invention relates to a base material for growing a single crystal diamond and a method for producing a single crystal diamond substrate.
2. Description of the Related Art
Diamond has a wide band gap of 5.47 eV and a very high dielectric breakdown electric field intensity of 10 MV/cm, and it has the highest thermal conductivity in materials. Therefore, if this is used for an electronic device, the device is advantageous as a high output power device.
Furthermore, the diamond has a high drift mobility and is the most advantageous as a high speed power device among semiconductors in comparison of Johnson performance index.
The diamond is thus said to be the ultimate semiconductor suitable for high frequency/high power electronic devices, and accordingly studies of various kinds of electronic devices using a single crystal diamond as a substrate have progressed.
Now, a single crystal diamond for producing a diamond semiconductor is, in many cases, the diamond referred to as an Ib type formed by a high-pressure-high-temperature method (HPHT) or an IIa type of which purity is enhanced.
However, it is difficult to grow in size, while the HPHT single crystal diamond having high crystallinity can be obtained. In addition, a price of the diamond becomes extremely high when its size becomes big and consequently, it is difficult to put it into practical use as the substrate for the devices.
In view of this, a CVD single crystal diamond formed by a vapor deposition method has been also studied to provide a low-cost single crystal diamond substrate having a large area.
Recently, there was reported a homoepitaxial CVD single crystal diamond that is homoepitaxially grown directly on the HPHT single crystal diamond base material (a seed base material) by the vapor deposition method (the 20th diamond symposium lecture summary (2006), pp. 6-7).
However, in this method, since the base material and the single crystal diamond grown are composed of the same material, it is difficult to separate these, and there are cost problems that the base material needs implanting ions in advance, a lengthy wet etching separation treatment after the growth and the like. There is also another problem that crystallinity of the single crystal diamond to be obtained deteriorates to a certain degree due to the ion implantation of the base material.
As an alternative, there was reported a CVD single crystal diamond heteroepitaxially grown by a CVD method on a single crystal iridium (Ir) film heteroepitaxially grown on a single crystal MgO base material (the seed base material) (Jpn. J. Appl. Phys. Vol. 35 (1996), pp. L1072-L1074).
However, in this method, there is a problem that the base material and the single crystal diamond grown are finely broken due to stress generated between the single crystal MgO substrate and the single crystal diamond grown via the single crystal Ir film (sum of internal stress and heat stress). Moreover, the crystallinity of the single crystal diamond to be obtained does not achieve a satisfactory level since crystallinity of an available single crystal MgO that is the seed base material is not sufficient.